I want to dye my hair red but it is already black. I have a prelightener but I don't know if I should wait a couple of days after I've done the prelightener before I put the red dye on or whether its OK to put it on straight away?

Once you've pre-lightened your hair, you can apply the desired color immediately.

I want to dye my hair red but it is already black. I have a prelightener but i don't know if i should wait a couple of days after i've done the prelightener before i put the red dye on or whether its ok to put it on straight away?
If your hair has been dyed black using a bleach lightner is the most effective way of removing this dark color... this is a very complex process and should only be attempted by a colorist you trust.